IAU Reclassified Pluto 20 Years Ago as Eris Discovery Forced 8-Planet Definition
Updated
Updated · Smithsonian Magazine · Aug 24
IAU Reclassified Pluto 20 Years Ago as Eris Discovery Forced 8-Planet Definition
3 articles · Updated · Smithsonian Magazine · Aug 24
Summary
Twenty years after the August 24, 2006 vote, Pluto’s downgrade to dwarf planet remains one of astronomy’s most disputed classification decisions.
The IAU acted after Eris was found in 2005, rejecting a proposal that would have expanded the solar system to 12 planets and instead defining a planet as a body that clears its orbit.
Pluto failed that third test because it shares its orbital neighborhood with Kuiper Belt objects, but planetary scientists including New Horizons lead Alan Stern still routinely call dwarf planets planets.
The controversy amplified public fascination rather than dimming it: Lowell Observatory still celebrates Pluto, and New Horizons’ 2015 flyby revealed an unexpectedly complex world with active geology and the heart-shaped Tombaugh Regio.
That attachment endures ahead of Pluto’s 2030 discovery centennial, with the IAU due to meet again in 2027 and NASA’s Jared Isaacman saying this year he was looking into restoring Pluto’s planet status.